There is concern in the aviation industry that portable electronic devices (PEDs) can interfere with mobile platform electronics systems (also referred to as avionics in mobile platform and space vehicle electronic applications). Mobile platforms as used herein include aircraft and space vehicles, as well as land-based and nautical transportation vehicles. Measurements of radiated energy levels in PEDs have been known to exceed earlier mobile platform equipment qualification standards, which afford less protection than current equipment standards and mobile platform certification requirements. This, combined with the increasingly widespread use of cell phones, could pose a threat to air safety.
There are two types of PEDs. First, there are those PEDs that intentionally transmit a signal, known as intentional transmitters. Intentional transmitters transmit a signal in order to accomplish their function. Intentional transmitters include cell phones; pagers; two-way radios; and remote-control toys. The second type of PED is the non-intentional transmitter. Non-intentional transmitters do not have to transmit a signal in order to accomplish their function. However, like most electrical devices, they emit some level of radiation. Examples of non-intentional transmitters include compact-disc players; tape recorders; hand-held games; laptop computers and personal digital assistants (PDAs); and laser pointers.
The Federal Aviation Administration (FAA) and other international aviation regulatory agencies have expressed concern that PEDs may interfere with navigational instruments aboard the mobile platform. There have been numerous anecdotal reports of incidents in which the use of PEDs apparently created anomalous or erroneous instrumentation signals in passenger mobile platform. The PEDs most frequently reported as being a source of interference are laptop computers. The most frequent mobile platform systems reportedly affected by a suspected PED interference source are the navigation systems. The FAA has implemented rules restricting the use of PEDs on commercial airlines. Such rules prohibit operation of a PED on an airplane unless the airline has determined that the device will not cause interference with the navigation or communication systems of the mobile platform. There are some exceptions, for example, portable voice recorders, hearing aids, heart pacemakers, and electric shavers, which may be used, and the rules do not apply at all in some cases, e.g., private planes flying under visual flight rules.
The FAA also recommends that the use of PEDs be prohibited during the takeoff and landing phases of flight below 10,000 feet, in order to avoid potential electronic interference with aircraft systems, and to avoid the potential for passengers to miss safety announcements. In response to the incidents and government regulations, airlines have attempted to restrict the use of portable electronic devices. Airline policies generally divide PEDs into three categories: those that may never be used, those that may always be used, and those that may be used only at certain times. PEDs such as hearing aids, pacemakers, electronic watches, and one-way pagers may generally be used at any time during flight. Conversely, most airlines prohibit certain PEDs at any time, e.g., AM/FM radios, television sets, two-way pagers, and CB radios. A third category of PEDs may be operated at specified times, i.e., prior to departure and after the mobile platform has reached an altitude of 10,000 feet. In particular, when the mobile platform is descending all PEDs in this category must be turned off. The PEDs subject to these restrictions include CD players, laptop computers, electronic video games, and GPS navigation sets. The pilot must be notified that all PEDs have been turned off before departure and/or descent. As for the use of cellular phones, many airlines permit passengers to place and receive calls onboard while the mobile platform is still at the gate. Otherwise, cell phones may not be used during airline takeoff and landings, or during flight.
As the use of passenger carry-on portable electronic devices (PEDs) becomes more prevalent, it may become considerably more difficult to maintain Electromagnetic Compatibility (EMC) between these devices and the mobile platform communications and navigation systems. The portability of these devices further makes it increasingly difficult to successfully implement traditional Electromagnetic Interference (EMI) solutions. The present invention provides a novel method and device with which to reduce or eliminate the potential for PED-to-mobile platform antenna coupled EMI that may occur through the coupling paths of the mobile platform fuselage window. The present invention may be implemented in new aircraft production as well as a retrofit application for aircraft in the field.
With the beginning of a multitude of inexpensive PEDs—i.e., electronic communications and data devices, it is likely that PEDs will consume more and more of the electromagnetic spectrum, whether by design, or unintentionally, e.g., in the form of harmonic or spurious signal emissions. In concert with an increase in the number of users and total emitter power, some of which utilize spread spectrum technology and increased power spectral content, mobile platform systems may be even more susceptible to EMI. Traditional mobile platform design does not incorporate EMI shielding in the mobile platform windows, thus allowing the possibility that electromagnetic energy can be coupled through the windows and into the externally-mounted mobile platform antennas. For example, the new Boeing 787 mobile platform design includes enlarged windows in the fuselage that may cause higher levels of PED-to-antenna coupled EMI through the windows.
As the quantity of PEDs in use during a flight increases, and in order to increase window size for passenger enjoyment, adequate space loss (attenuation) to mobile platform antennas may become nearly impossible. While traditional solutions, such as powering off of PEDs, may address interference at critical flight times, they do not address the potential for EMI during normal inflight conditions.
Choke ring ground planes have been employed in applications such as global positioning system (GPS) or various directional antennas, to reject multi-path signals from interfering with the primary signal being received by the antennas. As examples, U.S. Pat. No. 6,278,407 discloses dual-frequency choke-ring ground planes having an antenna mounted in the center of multiple grooved surfaces, and an electromagnetic filter structure which makes the depth of each groove appear to be different for each of two frequency bands, and also discloses using a groove depth which is either slightly less than a quarter-wavelength or greater than a quarter-wavelength of the second bandwidth L2. Also, U.S. Pat. No. 6,040,805 discloses a low profile ceramic choke for GPS antenna systems having concentric ring segments arranged coaxially about a circular antenna.
While the metallic structure of the fuselage provides shielding between internal EMI and externally mounted antennas, the windows that are positioned along the walls of the fuselage for passenger enjoyment do not adequately shield EMI from interfering with external antennas. Moreover, as mobile platform are designed to be more aesthetically pleasing to passengers, many mobile platform are designed with even larger windows. Therefore, there is a need for a means of attenuating signals that are generated within an enclosed structure such as a mobile platform, from interfering with the operation of external antenna from receiving direct signals, for example, navigation or communications signals from ground-based or satellite-based sources.